Adjustable motor standoffs, by Dualsky.
Does your R/C airplane have a long cowl? Need to move the motor just a bit further forward from the firewall to get the Center of Gravity on that gas to electric conversion? These will come in handy. Able to be shortened or lengthened with several included shims, they will fit a variety of aircraft. The wider end goes up against the firewall while the narrower end goes up against your motor's mounting plate.